Petroleum is an indispensable source for energy and chemicals. At the same time, petroleum and petroleum based products are also a major source for air and water pollution. To address growing concerns with pollution caused by petroleum and petroleum based products, many countries have implemented strict regulations on petroleum products, particularly on petroleum refining operations and the allowable concentrations of specific pollutants in fuels, such as, sulfur content in gasoline fuels. For example, motor gasoline fuel is regulated in the United States to have a maximum total sulfur content of less than 15 ppm sulfur.
Due to its importance in our everyday lives, demand for petroleum is constantly increasing and regulations imposed on petroleum and petroleum based products are becoming stricter. Available petroleum sources currently being refined and used throughout the world, such as, crude oil and coal, contain much higher quantities of impurities (such as, compounds containing sulfur). Additionally, current petroleum sources typically include large amounts of heavy hydrocarbon molecules, which must be converted to lighter hydrocarbon molecules through expensive processes like hydrocracking, for eventual use as a transportation fuel.
Current conventional techniques for petroleum upgrading include hydrogenative methods which require an external source of hydrogen in the presence of a catalyst, such as hydrotreating and hydrocracking. Thermal methods performed in the absence of hydrogen are also known in the art, such as coking and visbreaking.
Conventional methods for petroleum upgrading, however, suffer from various limitations and drawbacks. For example, hydrogenative methods typically require large amounts of hydrogen gas to be supplied from an external source to attain desired upgrading and conversion. These methods can also suffer from premature or rapid deactivation of catalyst, as is typically the case during hydrotreatment of a heavy feedstock and/or hydrotreatment under harsh conditions, thus requiring regeneration of the catalyst and/or addition of new catalyst, which in turn can lead to process unit downtime. Thermal methods frequently suffer from the production of large amounts of coke as a byproduct and a limited ability to remove impurities, such as, sulfur and nitrogen. This in turn results in the production of large amount of olefins and diolefins, which may require stabilization. Additionally, thermal methods require specialized equipment suitable for severe conditions (such as, compounds containing sulfur), require the input of significant energy, thereby resulting in increased complexity and cost.
As noted above, the provision and use of an external hydrogen supply is both costly and dangerous. Alternative known methods for providing hydrogen by in-situ generation method, including partial oxidation, and production of hydrogen via a water-gas shift reaction. Partial oxidation converts hydrocarbons to carbon monoxide, carbon dioxide, hydrogen and water, as well as partially oxidized hydrocarbon molecules such as carboxylic acids; however, the partial oxidation process also removes a portion of valuable hydrocarbons present in the feedstock and can cause severe coking.
Thus, there exists a need to provide a process for the upgrading of hydrocarbon feedstocks that do not require the use of a catalyst or an external hydrogen supply. Methods described herein are suitable for the production of more valuable hydrocarbon products having one or more of a higher API gravity, higher middle distillate yields, lower sulfur content, and/or lower metal content via upgrading with supercritical water without requiring any use of a hydrothermal reactor catalyst or the external supply of hydrogen.